Manual:$wgFallbackSkin

From Linux Web Expert

<translate> Skins</translate>: $wgFallbackSkin
Fallback skin used when the skin defined by $wgDefaultSkin can't be found.
<translate> Introduced in version:</translate>1.24.0 (Gerrit change 148424; git #Ibd7485d)
<translate> Removed in version:</translate><translate> still in use</translate>
<translate> Allowed values:</translate>(string)
<translate> Default value:</translate>'fallback'